International telephone calls sometimes cannot be placed successfully. Called parties may be on the telephone or there may be congestion, so the line cannot be reached. Sometimes the calling party dials a non-existent number or there is an equipment failure in the foreign network. To address these issues, AT&T Corp. has developed an international redial service known under the trademark "AIR" (AT&T International Redial). This international redial service allows callers who are unsuccessful in completing international telephone calls to have the service automatically redial the call. The service typically plays a short message such as "if you would like to use AT&T International Redial Service, please press *234." If the caller presses *234, the redial service automatically attempts to redial the call (e.g., up to ten times in a half hour period.)
When a caller places an international call, the AT&T telephone network determines whether or not the caller is an international redial service subscriber based on calling party identification information that is passed automatically to the network. If the caller is a subscriber to the international redial service, the network passes the call to a network adjunct. The adjunct handles initial call processing, such as determining the language used by the subscriber and determining whether redial service is available to the destination foreign country. Following this initial call processing, call handling is returned to the telephone network for call completion. If an international call cannot be completed, the caller is typically alerted with a short message (e.g., "your call cannot be completed as dialed") or a busy tone.
Under the international standards promulgated by the International Telecommunications Union (ITU), foreign networks may provide certain unsuccessful call reason information to the telephone network that identify the cause of the call completion failure. The format of the unsuccessful call reason information depends upon the standardized signaling format used by the foreign telephone network to indicate call completion failures. For example, some countries, such as the United Kingdom use the ISUP (ISDN or Integrated Services Digital Network User Part) signaling system in which call failures are indicated by the generation of an appropriate "cause value" number. Other countries, such as France, use the TUP (Telephone User Part) signaling system in which call failures are indicated by the generation of an appropriate "signal code." Still other countries use the R2 (Register-Signaling 2) signaling system in which "B-signal" codes are issued when calls fail. If TUP signal codes or other non-ISUP codes are received by the telephone network's International Switching Center, such codes are typically translated into ISUP-type codes, if the telephone network uses ISUP signaling internally. For example, a TUP address incomplete signal code (No. 4) may be translated into an ISUP address incomplete cause value (No. 28) and a TUP unallocated number signal code (No. 7) may be translated into an ISUP unallocated number cause value (No. 1). Call completion failure information such as ISUP cause value information, TUP signal code information, R2 B-signal information, and other suitable call completion failure information provided by a foreign network when an international call is not completed is hereinafter referred to as "unsuccessful call reason information."
The ITU-T (formerly CCITT--Commite' Consultatif International de Telegraphique et Telephonique) Recommendations set forth individual reasons for call completion failure such as "user busy," "incomplete number," "switching equipment congestion," etc. These reasons are conveyed as signals in the modern international signaling systems which are recommended by the ITU-T. For example, the ISUP signaling system can convey up to 127 unsuccessful call reasons in the form of cause values (e.g., "user busy"--cause value number 17, "invalid number format" --cause value number 28, switching equipment congestion--cause value number 42, etc.) Although the telephone network may use unsuccessful call reasons returned by the foreign network (e.g., to determine whether to provide a busy signal or to play a message), the adjunct that supports the international redial service was previously only able to recognize the unsuccessful call reason corresponding to the "user busy" condition (cause value number 17 in the ISUP signaling system).
If the adjunct determined that the cause of the call completion failure was the "user busy" condition, the adjunct could promptly play a message asking the user to press *234 to invoke the automatic redial feature. However, because the adjunct could not identify call completion failures other than the "user busy" condition, the adjunct had to rely on the expiration of a timer to determine whether or not to offer the international redial service in all other cases. If the timer expired and the call had not been completed, the adjunct typically played the standard redial service message (i.e., "if you would like to use AT&T International Redial Service, please press *234").
There are at least two possible disadvantages associated with the international redial service just described. First, offering the redial service when the cause for the call completion failure is the dialing of a non-existent number is inappropriate, because redialing a non-existent number is counterproductive. In such situations, it would be better if the redial service offer could be inhibited. Second, although the adjunct is able to respond quickly and appropriately by offering redial service when an unsuccessful call reason "user busy" is detected, there are many additional causes of call completion failures where a similar response is desired. For example, if a call completion failure is due to switching equipment congestion, it would be desirable if the adjunct could recognize this reason and promptly offer the redial service without waiting for a timer to expire.
It is therefore an object of the present invention to provide a system with improved international telephone call redial services.